Latest: Micheál Martin said there has to be a 'fundamental change in the direction of housing'.
But they will uphold the confidence and supply agreement until after the Budget to see that change.
The Fianna Fáil leader says they need to see significant changes in how the state intervenes in providing affordable homes.
Housing is one of the party's key budget issues and negotiations are underway with Fine Gael ahead of Budget 2019.
Deputy Martin said they are not Ministers and cannot implement the necessary policies they think are needed in housing.
"We've already affected some changes in terms of housing, in terms of HAP payments and allowances.
"But we also said that the confidence and supply, we're going to uphold because we do believe that is important in the broader sense in how the country is run, but we're not in an executive position."
Update: Fianna Fáil have said this budget 'has to be a housing budget'.
Housing spokesperson Darragh O'Brien says they're not making ultimatums when it comes to renewing the confidence and supply agreement.
This budget is the third and final under the current agreement.
But Deputy O'Brien says the Government knows what will happen if housing is not a priority in Budget 2019.
"I don't want to be setting down any red lines but the bottom line is, Michéal Martin has said it, I've said it, and my colleagues have said it, this has to be a housing budget.
"We've started those negotiations, I want to be positive about that, but I want to give a clear message to Fine Gael and those who support them in Government that housing, delivery of social housing, ending of homelessness, and affordable housing is an absolute priority for us as a party."
Earlier: Fianna Fáil TDs and senators will meet in Dublin today as the parliamentary party prepares for the return of the Dáil next week.
Budget 2019 - the final one under the confidence and supply agreement - will be one of the main topics at the annual think in.
Brexit, housing, health and the Budget are among the key issues set to dominate their discussions.
British academic Tim Bale will also address members on the Brexit negotiations.
The party is meeting in Malahide in Dublin today and tomorrow.
Fianna Fail's think-in comes just weeks ahead of the Budget and just before the Dail resumes after the summer recess.
Michael Martin has yet to meet the Taoiseach to discuss extending the deal, but Fianna Fail deputy leader Dara Calleary has said the Government need to be more honest when it comes to issues such as health and housing before negotiating any sort of extension to it.